At least one photo captured the (partial) trail of the Falcon Heavy during launch. As in other rocket launches, it visualizes different conditions in atmospheric layers at different altitudes.

There will likely appear video material about the launch that clears up the question if the trail ceased to form at the upper end as seen here - or if the gap between rocket and trail is just very large.

I was curious about the fuel used in the Falcon Heavy. It turns out to be very similar to jet fuel, but much more highly purified:

RP-1 (alternately, Rocket Propellant-1 or Refined Petroleum-1) is a highly refined form of kerosene outwardly similar to jet fuel, used as rocket fuel.
...Alkenes and aromatics were held to very low levels. These unsaturated hydrocarbons tend to polymerize not only at temperature, but during long periods of storage. At the time, it was thought that kerosene-fueled missiles might remain in storage for years awaiting activation. This function was later transferred to solid-fuel rockets, though the high-temperature benefits of saturated hydrocarbons remained. Because of the low alkenes and aromatics, RP-1 is less toxic than various jet and diesel fuels, and far less toxic than gasoline.

The more desirable isomers were selected or synthesized. Linear alkanes were removed in favor of highly branched and cyclic molecules. This increased resistance to thermal breakdown, much as these isomer types improve octane rating in piston engines. Jet engines and heating and lighting applications, the prior users of kerosene, had been much less concerned with thermal breakdown and isomer contents. The most desirable isomers were polycyclics, loosely resembling ladderanes.

In production, these grades were processed tightly to remove impurities and side fractions. Ashes were feared likely to block fuel lines and engine passages, as well as wear away valves and turbopump bearings lubricated by the fuel. Slightly too-heavy or too-light fractions affected lubrication abilities, and were likely to separate during storage and under load. The remaining hydrocarbons are at or near C12 mass. Because of the lack of light hydrocarbons, RP-1 has a high flash point, and is less of a fire hazard than gasoline/petrol or even some jet and diesel fuels.

Basically it's almost pure hydrocarbon, and is burned using liquid oxygen as the oxidiser. In theory that should produce almost exclusively carbon dioxide plus water as the exhaust products, so we are definitely seeing a contrail here rather than smoke.

I was curious about the fuel used in the Falcon Heavy. It turns out to be very similar to jet fuel, but much more highly purified:

RP-1 (alternately, Rocket Propellant-1 or Refined Petroleum-1) is a highly refined form of kerosene outwardly similar to jet fuel, used as rocket fuel.
...Alkenes and aromatics were held to very low levels. These unsaturated hydrocarbons tend to polymerize not only at temperature, but during long periods of storage. At the time, it was thought that kerosene-fueled missiles might remain in storage for years awaiting activation. This function was later transferred to solid-fuel rockets, though the high-temperature benefits of saturated hydrocarbons remained. Because of the low alkenes and aromatics, RP-1 is less toxic than various jet and diesel fuels, and far less toxic than gasoline.

The more desirable isomers were selected or synthesized. Linear alkanes were removed in favor of highly branched and cyclic molecules. This increased resistance to thermal breakdown, much as these isomer types improve octane rating in piston engines. Jet engines and heating and lighting applications, the prior users of kerosene, had been much less concerned with thermal breakdown and isomer contents. The most desirable isomers were polycyclics, loosely resembling ladderanes.

In production, these grades were processed tightly to remove impurities and side fractions. Ashes were feared likely to block fuel lines and engine passages, as well as wear away valves and turbopump bearings lubricated by the fuel. Slightly too-heavy or too-light fractions affected lubrication abilities, and were likely to separate during storage and under load. The remaining hydrocarbons are at or near C12 mass. Because of the lack of light hydrocarbons, RP-1 has a high flash point, and is less of a fire hazard than gasoline/petrol or even some jet and diesel fuels.

Basically it's almost pure hydrocarbon, and is burned using liquid oxygen as the oxidiser. In theory that should produce almost exclusively carbon dioxide plus water as the exhaust products, so we are definitely seeing a contrail here rather than smoke.

Click to expand...

Paraffin worked for the Russians, better than producing all the pollutants of the Space Shuttle boosters.

"All Soyuz rockets use RP-1 and liquid oxygen (LOX) propellant, with the exception of the Soyuz-U2, which used Syntin, a variant of RP-1"